In measuring technology, process data may be picked up or recorded in physical locations that may differ from those where this process data, for example measured values or process variables, may be subsequently displayed and further processed. For example, in an industrial plant, containers whose fill levels or pressures may be to be picked up can be distributed over an extended industrial area. The fill levels or pressures should, however, be able to be monitored from a central control room, and for these reasons the measured values or process variables may be transmitted from the locations of measuring to said central control room.
Various solutions for transmitting process data may exist. For example, dedicated lines may be able to be used in order to transmit process data by means of the 4-20 mA technology. The 4-20 mA technology may, for example, be used in two-wire measuring devices or four-wire measuring devices. In such measuring arrangements the material-related expenditure in particular for cabling may be high. In order to connect the dedicated lines of the measuring devices to a central control room, star-shaped cabling may be necessary.
Furthermore, bus systems may exist that may make it possible, on a common medium, a shared medium, a common net infrastructure or a bus, to distribute the process data to the sensors, actuators, field devices, control devices or process control computers or process main computers that in each case are connected to the bus. The commonly used bus and the shared bus, respectively may contribute to a reduction in materials and to minimising service and maintenance for the cabling. A net infrastructure may be a network infrastructure.
In recent times, radio systems may have been developed that may make it possible to essentially do without cabling or to abandon cabling, and instead of cabling to use the air as a so-called shared medium.
Since with using a shared medium it may be possible that each participant, each field device, each actuator or each sensor can access the shared medium, and thus to be able to occupy the shared medium, a rulebased procedure for access to the bus may have been developed. In order to make such a procedure or sequence possible, a bus participant or a field device may be configured as a so-called master, while other field devices may be configured as so-called slaves. The master may control the access to the bus, and in particular the access to a slave or to a plurality of slaves that may be connected to the shared medium.
In master-slave communication, a request telegram may be sent to a slave which slave can respond to this request telegram by means of a response telegram. If several slaves exist, or if a plurality of slaves exist, then these slaves may be able to be requested consecutively by the master.
If a master communicates with several slaves, then it may happen that a slave interprets the response of another slave as the beginning of a request telegram of the master. In order to essentially prevent such misinterpretation, an access regulation, an access ruling and access control, respectively to the shared medium may be necessary. Access control may consist in that each communication participant, prior to the dispatching of a request, or prior to the dispatching of a response, in each case may wait for a predetermined waiting time and waiting period, respectively before access to the shared medium can take place. Such a waiting period may also be referred to as a timeout period respectively timeout time. In other words, prior to the dispatching of a request or a response via the shared medium, a master and/or a slave may have to wait for a timeout period before access to the shared medium can take place.
To ensure that essentially all the communication participants that are connected to a shared medium and, in particular, that are involved in communication may be ready to receive at the point in time when at least one of the participants begins with the transmission of a telegram, a timeout control respectively a timeout regulation may be present in the field devices. This timeout control respectively this timeout control device may control or drive waiting for a timeout time predetermined by the respective system prior to dispatching the request or the response, in other words prior to access to the bus. However, as a result of this timeout time or waiting time the data throughput on the shared medium may be low.
There may thus exist a need to make more effective communicating between field devices possible.